The carbon steel feedwater piping at a waste-to-energy plant was suffering from wall thinning and leaking after being in service for approximately six years. Metallographic examination of ring sections removed front the piping revealed a normal microstructure consisting of pearlite and ferrite. However, the internal surface on the thicker regions of the rings exhibited significant deposit buildup, where the thinned regions showed none. No significant corrosion or pitting was observed on either the internal or external surface of the piping. The lack of internal deposits on the affected areas and the evidence of flow patterns indicated that the wall...